Process to recover pure copper during purification of zinc sulfate solution

Abstract

A process for recovery of copper from a copper residue obtained during purification of a zinc sulfate solution comprises leaching the copper residue in a concentrated sulfuric acid solution in the presence of an oxidant at a temperature of between 60 DEG and 80 DEG C. and separating the solids from the leach solution, electrowinning copper from the leach solution, returning the electrolyte solution to the initial leaching stage to initiate dissolution of the copper residue, and bleeding a portion of the electrolyte solution to reduce the concentration of impurities in the solution.

We claim: 
     
       1. Process for recovery of copper from a copper residue obtained during purification of a zinc sulfate solution and containing about 50% copper and minor amounts of cadmium and zinc, said process comprising: a) atmospheric leaching the copper residue in a concentrated sulfuric acid solution in the presence of an oxidant at a temperature of between 60° and 80° C. to produce a leach solution and separating the solids from the leach solution;   b) electrowinning copper from the leach solution to produce an electrowon solution;   c) returning the electrowon solution to the initial leaching stage (a) to initiate dissolution of the copper residue; and   d) bleeding a portion of the electrowon solution to reduce the concentration of impurities in the solution.   
     
     
       2. Process as defined in claim 1, wherein purification of the zinc sulfate solution is done in at least a first stage and a second stage, wherein in the first stage the zinc sulfate solution is treated with the zinc dust and an antimony compound to form a cement containing essentially copper and cadmium, and separating said cement from such partially purified solution, and wherein in the second stage the partially purified solution is treated with zinc dust and an antimony compound to form a cement containing essentially cobalt, and separating said cement from the purified solution. 
     
     
       3. Process as defined in claim 2, wherein the major portion of the cement from the second stage is recycled to the first stage to be used therein instead of zinc dust for the treatment of the zinc sulfate solution. 
     
     
       4. Process as defined in claim 2, wherein the cement from the first stage is filtered in vacuum drum filters to remove the solids from the filtrate, and the solids leached with sulfuric acid and passed through a filter press to produce said copper residue and a filtrate containing cadmium for further treatment. 
     
     
       5. Process as defined in claim 4, wherein a minor amount of nickel is present in the copper residue and wherein at least 25% of said copper residue is mixed with said filtrate at a temperature of about 95° C. and treated with zinc dust to which purification zinc residue is added to adjust the pH to about pH 4 to cement the nickel. 
     
     
       6. Process as defined in claim 5, wherein said cement is washed with water at 70° C. to solubilize nickel and part of the cobalt which are subsequently eliminated by neutralization and disposal and wherein the residue obtained after washing is recycled back to the initial leaching stage (a). 
     
     
       7. Process as defined in claim 5, wherein the liquid phase from the cementation stage is treated with KMnO 4  at about 95° C. to precipitate Co, Tl, and Pb impurities and filtered, and wherein the filtered liquid is further treated to recover cadmium.